Researchers followed the leaf through production—and found the highest PAH levels during drying

Fresh yerba mate cannot move directly from the tree into your cup. After harvesting, the leaves must be heated and dried to stop natural decomposition, reduce moisture, and prepare them for aging and milling.

How that heat reaches the leaf matters.

In traditional yerba mate production, wood is often burned to generate the heat used during sapeco—the initial rapid-heating stage—and final drying. When the leaves come into direct contact with smoke and combustion gases, substances created by burning wood can be deposited on their surface.

A 2010 study led by Manoela Alano Vieira examined what happens to polycyclic aromatic hydrocarbons, or PAHs, as yerba mate moves through these processing stages.

The results reveal an important distinction: PAHs are not simply an unavoidable characteristic of the yerba mate plant. Their concentration can increase during processing, with the highest levels appearing during drying.

What Are PAHs?

Polycyclic aromatic hydrocarbons are a large group of chemical compounds formed when organic material does not burn completely.

They can be produced by:

• Burning wood

• Tobacco smoke

• Vehicle exhaust

• Grilling or charring food

• Industrial combustion

• Direct smoke-drying processes

PAHs are common environmental contaminants, so small amounts can be present in air, water, soil, and food. However, some production methods can add significantly more of them.

Not every PAH carries the same level of concern, but members of this chemical family include compounds associated with toxic, mutagenic, and carcinogenic effects. This makes controlling unnecessary PAH contamination an important food-processing and quality issue.

Following Yerba Mate Through Production

Vieira and her research team wanted to identify when PAHs enter yerba mate during manufacturing.

Rather than examining only the packaged product, they collected samples at different stages of production. This allowed them to measure how PAH concentrations changed as the leaves moved through the process.

The key stages included:

1. Freshly harvested material
   Leaves and small branches arrive from the farm.

2. Sapeco
   The plant material is exposed to intense heat for a short period. This stops enzymatic activity and helps preserve the leaf.

3. Drying
   Moisture is reduced until the yerba is stable enough for storage and aging.

4. Finished material
   The dried yerba can then be milled, aged, blended, and packaged.

Both sapeco and drying traditionally involve wood combustion. Depending on the equipment, the leaves may come into direct contact with flame, smoke, or combustion gases.

That contact creates the opportunity for PAHs formed by burning wood to settle onto the yerba mate.

What the Researchers Found

Across the samples, total PAH concentrations ranged from 443 to 9,001 micrograms per kilogram.

The most important finding was where the highest concentrations appeared:

“The highest PAHs levels [were] recorded during the mate drying step.”

In other words, the drying stage produced the greatest measured PAH burden.

The researchers concluded that the manufacturing process used in conventional yerba mate production can increase PAH concentrations in the finished product.

This establishes a direct connection between the processing method and the chemical contaminants measured on the leaf.

Why Drying Creates the Greatest Opportunity for Contamination

Drying is not a momentary event.

While sapeco exposes the leaves to intense heat for a short time, final drying can continue for hours. If wood smoke or combustion gases move through the same space as the yerba mate, the leaves remain exposed throughout this period.

Yerba mate also presents a large surface area. Every leaf fragment and small stem creates another surface on which airborne compounds can settle.

The combination of prolonged exposure, circulating combustion gases, and extensive leaf surface helps explain why PAHs can accumulate during this stage.

The process accomplishes the necessary goal of removing moisture, but direct smoke exposure may introduce compounds that were not naturally part of the harvested leaf.

Heat and Smoke Are Not the Same Thing

Yerba mate must be heated and dried. Smoke exposure is not required to accomplish that purpose.

This distinction is fundamental.

In a direct-smoke system, the same combustion stream used to generate heat may reach the leaves. Smoke, particles, and combustion compounds can therefore come into contact with the product.

In an indirect hot-air system, heat is transferred without allowing the leaves to touch smoke or combustion gases. The leaves still dry, but the heat source and the product remain separated.

The objective is not to eliminate drying. It is to control what reaches the leaf during drying.

Processing Becomes Part of the Product

Two yerba mate products may begin with the same plant and still reach the consumer with different chemical profiles.

The difference may come from what happens after harvest:

• The fuel used to create heat

• Whether combustion is complete or incomplete

• The distance between the fire and the leaves

• The length of the drying cycle

• Whether smoke is filtered

• Whether the heating system keeps combustion gases away from the product

Processing is therefore not merely a technical step behind the scenes. It becomes part of the finished yerba mate.

A smoky character may be considered traditional or desirable by some consumers. But smoke also carries compounds that can remain on the leaf. The sensory effect and the contamination risk originate from the same physical contact.

A More Controlled Approach

The Vieira study demonstrates that PAH contamination can rise as yerba mate moves through production and that drying is the most consequential stage.

Its central lesson is straightforward:

The way the leaf is dried changes what remains on the leaf.

Using indirect hot air allows producers to achieve the necessary reduction in moisture without intentionally exposing the yerba mate to smoke or combustion gases.

It is a more controlled way to protect the character of the harvested plant—and to avoid adding contaminants that do not need to be there.

Yerba Quantica is Air-Dried, unsmoked, preserving the health of our consumers and the  benefits integrity of the leaves.

The leaf needs heat. It does not need smoke.

Original research: Manoela Alano Vieira, Marcelo Maraschin, Angela Angeloni Rovaris, Renata Dias de Mello Castanho Amboni, Cristiane Manfé Pagliosa, José Júnior Mendonça Xavier, and Edna Regina Amante, “Occurrence of Polycyclic Aromatic Hydrocarbons Throughout the Processing Stages of Erva-Mate (Ilex paraguariensis),” Food Additives & Contaminants: Part A, Volume 27, Issue 6, 2010.

Read the original peer-review article